1. Field of the Invention
The present invention relates to a tunable wavelength optical filter, more particularly, to an active type tunable wavelength optical filter having a Fabry-Perot structure.
2. Description of the Prior Art
Among micro electromechanical systems (MEMS) based on a semiconductor process technique, an active type optical filter for wavelength division multiplexing (WDM) is applied to an optical communication. Recently, it is used in an optical signal dividing and multiplexing device for a massive information network such as Internet. Such optical filter has a function of dividing an input signal, which is in an optical wavelength multiplexing transmitting method, into output signals by the wavelength region. Particularly, in order to implement a dynamic WDM system, it is a key to manufacture the active type tunable wavelength optical filter operated at a high speed. Various techniques of manufacturing the tunable wavelength filter for implementing the dynamic WDM system were suggested. But, among them, in case of a piezo-electric transducer filter of adjusting a gap between two pairs of Fabry-Perot micro-mirrors by a piezo material, it has a limitation in the application thereof, because of the physical instability of a used material and a slow response characteristics. In addition, a Mach-Zender optical filter using an optical interference phenomenon is accomplished by manufacturing an optical waveguide and a phase modulator on a semiconductor substrate, but has a problem that the structure thereof is complicated and it is difficult to manufacture that. In order to improve the previous method of manufacturing the filter, the active type tunable wavelength filter having the MEMS structure of which the response speed is relatively quick and the manufacture technique is easy as the semiconductor process technique has been suggested.
On the other hand, in a piezo-type FP filter or a tunable filter having a Fiber Bragg Grating carved in an optical fiber, which is currently commercial, since a tuning speed is slow at the level of msec or the tunable wavelength band is narrow, it is impossible to use that to the active type network device. However, the MEMS type tunable filter using an electrostatic force as a driving source accomplishes the response speed below few tens microsecond (μs) and the tunable wavelength band of the order of 100 nm, thereby it can be applied to the current optical communication system. However, the MEMS type tunable filter of gallium-arsenide substrate suggested currently has problems that a consistent process can not be performed like the silicon wafer process due to difficulties of the manufacturing process and the packaging technique.